Calmodulin inhibitor

Recrystd from abs EtOH dried in vacuo and stored in tightly stoppered bottles because it is hygroscopic. It is soluble in H2O but insoluble in CgHg, Et20 and alkaline aqueous soln. It has UV at 258 and 307.5nm (log e 4.50 and 3.50) in EtOH (neutral species). [Craig et al. J Org Chem 22 709 1957.] It is a calmodulin inhibitor [Levene and Weiss J Parmacol Exptl Ther2Q% 454 1978], and js a psychotropic agent [Fowler Arzneim.-Forsch 27 866 1977]. 

Similar to nNOS, Ca2+-activated calmodulin is important for the regulation of eNOS activity. However, several other proteins interact with eNOS and regulate its activity. Heat shock protein 90 (hsp90) is found associated with eNOS and probably acts as an allosteric modulator that activates the enzyme. Caveolin-1 binds eNOS and directs it to caveolae. Caveolin-1 is viewed as an inhibitor of eNOS activity, which is being replaced by CaM upon activation of endothelial cells [2]. 

Figure 6. A hypothetical scheme for the control of the number of active crossbridges in smooth muscle. Following the activation of a smooth muscle by an agonist, the concentrations of intermediates along the main route begins to build up transiently. This is shown by the thickened arrows. Also, cAMP is generated which is universally an inhibitor in smooth muscle. Cyclic AMP in turn combines with protein kinase A, which accounts for most of its action. The downstream mechanisms, however, are not well worked out and at least three possibilities are likely in different circumstances. First, protein kinase A is known to catalyze the phosphorylation of MLCK, once phosphorylated MLCK has a relatively lower affinity for Ca-calmodulin so that for a given concentration of Ca-calmodulin, the activation downstream is reduced. The law of mass action predicts that this inhibition should be reversed at high calcium concentrations. Other cAMP inhibitory mechanisms for which there is evidence include interference with the SR Ca storage system, and activation of a MLC phosphatase.

So far, it has been established from in vitro studies that the enzyme undergoes phosphorylation, a process that changes the conformation of the enzyme protein and leads to an increase in its activity. This involves Ca +/calmodulin-dependent protein kinase II and cAMP-dependent protein kinase which suggests a role for both intracellular Ca + and enzyme phosphorylation in the activation of tryptophan hydroxylase. Indeed, enzyme purified from brain tissue innervated by rostrally projecting 5-HT neurons, that have been stimulated previously in vivo, has a higher activity than that derived from unstimulated tissue but this increase rests on the presence of Ca + in the incubation medium. Also, when incubated under conditions which are appropriate for phosphorylation, the of tryptophan hydroxylase for its co-factor and substrate is reduced whereas its Fmax is increased unless the enzyme is purified from neurons that have been stimulated in vivo, suggesting that the neuronal depolarisation in vivo has already caused phosphorylation of the enzyme. This is supported by evidence that the enzyme activation caused by neuronal depolarisation is blocked by a Ca +/calmodulin protein kinase inhibitor. However, whereas depolarisation... 

The cAMP and Ca2+ pathways also interact at the level of protein kinases and protein phosphatases. This is illustrated by inhibitor-1 and DARPP-32, which are phosphorylated and activated by PKA and then inhibit PP1, which can dephosphorylate numerous substrates for Ca2+-dependent protein kinases. Another example is the physical association between PKA and PP2B (a Ca2+/ calmodulin-activated enzyme) via the AKAP-anchoring proteins. 

Because of its ability to bind CaM, tamoxifen can increase cyclic AMP surges by inhibiting cyclic AMP hydrolysis by the Ca2+-calmodulin-dependent cyclic nucleotide phosphodiesterase (Fanidi et al. 1989 Rowlands et al. 1990). In bovine brain preparations, tamoxifen appears to act as a competitive inhibitor of calmodulin-activated phosphodiesterase with an IC50 of 2 p,M, similar to the value reported for trifluoperazine under the same experimental conditions (Lam 1984). 

Schini.V. B., Vanhoutte, P. M., Inhibitors of calmodulin impair the constitutive but not the inducible nitric oxide synthase activity in the rat aorta, J. Pharmacol. Exp. Then 261 (1992), p. 553-559... 

While all of these events are interconnected, the two most critical are neuronal rapid influx of Ca2+ and activation of nNOS, both which trigger all downstream events. Therefore, directly blocking the toxic effects of glutamate /NO, can be achieved through many means, including selective nNOS inhibitors, Ca2+ channel blockers [NMDA, Kainate/AMPA] [ryanodine-sensitive, IP3], calmodulin antagonists, Ca2+... 

A human gene for hepatic inducible NOS was isolated in 1993 by Geller and coworkers76. Hepatocytes were isolated from an operative wedge resection, which were over 98% pure. The cells were stimulated with cytokines TNF-a, IL-1 and IFN-y. The purified cDNA, in addition to FMN, FAD and NADPH factors, also contained a calmodulin site. This site retained some activity in the presence of calcium inhibitors. There are also phosphorylation sites at 232, 576 and 890 residues. 

Makarov AA, Tsvetkov PO, Villard C, Esquieu D, Pourroy B, Fahy J, Braguer D, Peyrot V, Lafitte D. (2007) Vinflunine, a novel microtubule inhibitor, suppresses calmodulin interaction with the microtubule-associated protein STOP. Biochemistry 46 14899-14906. 

PHYTOTOXIC COMPOUNDS WITH CALMODULIN INHIBITOR PROPERTIES FROM SELECTED MEXICAN FUNGI AND PLANTS... 

Phytotoxic Compounds with Calmodulin Inhibitor Properties 429... 

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